Accelerometers, acceleration switches, and inertial sensing devices are widely used to measure accelerations (forces resulting from vibrations, changes in velocity, or the like). Such devices may include some sort of sensing mass suspended within the device so as to be affected by acceleration forces so as to move and thereby open or close an electrical contact. The acceleration switch may be filled with damping fluid so as to prevent premature opening or closing of the switch due to vibration, shocks, or the like. Examples of such acceleration switches are illustrated in U.S. Pat. Nos. 2,997,883, 3,096,411 and 3,715,535.
When an acceleration switch is used to generate a timing signal, it may be necessary to provide a very precisely timed output. For example, in a reentry vehicle such as might be used in entering the earth's atmosphere, it may be desirable to know within milliseconds the precise moment when a preset acceleration level is reached. If the movement of the mass is damped by fluid, an unacceptable lag may occur in closing the switch. On the other hand, if the mass is undamped, vibration or shock may close the switch prematurely.
In order that the mass move relatively freely within the device, low friction bearings such as ball bearings have been employed in the suspension of the mass. Such bearings may be relatively weak and may break upon heavy lateral shock loading; thus preventing reliable switch operation.